AGN and Quasar Clustering at z=0.2-1.5: Results from the DEEP2 + AEGIS Surveys. Alison Coil Hubble Fellow University of Arizona. Chandra Science Workshop November 2006. Main Points.
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AGN and Quasar Clustering at z=0.2-1.5: Results from the DEEP2 + AEGIS Surveys
University of Arizona
Chandra Science Workshop
Different QSO/AGN formation theories predict different clustering with luminosity (host and/or QSO) and host color - clustering constrains models
QSOs cluster more like blue than red galaxies at z~1 (seen using local overdensity measure as well)
Chandra AGN cluster more like red than blue galaxies at z~0-1, see evidence for luminosity-dependence in clustering as well
4. Cross-correlating with large samples of galaxies rather than using QSO/AGN samples alone gives smaller errors - both Poisson and cosmic variance
DEEP2 is a completed redshift survey using the Keck II telescope, covering multiple fields on the sky (for cosmic variance) to study galaxy evolution and LSS at z=0.7-1.5.
One field isthe Extended Groth Strip (EGS), which has 8 Chandra pointings of 200 ks each over a 2 x 0.25 degree field, with redshifts from z=0.2-1.5 in this field to RAB=24.1.
DEEP2 has a high sampling rate (60%) and precise redshifts (<70 km/s) - good for clustering and environments. Full sample has 50,000 galaxies over 3 sq. degrees.
EGS has 10,000 galaxies in 0.5 sq. degrees.
(Chandra team: K. Nandra, A. Georgakakis, E. Laird)
Chandra & XMM:
Spitzer MIPS, IRAC
Background: 2 x 2 deg
DEEP2 spectra and Ks imaging
V,I (Cycle 13)
VLA - 6cm + 21cm SCUBA
Trace different physics on different scales:
Smallest scales (r < 100 kpc/h): mergers + galaxy-galaxy interactions
Intermediate scales (100 kpc/h < r < 2 Mpc/h): radial profiles of galaxies w/in halos / groups and clusters
Large scales (r > 2 Mpc/h): large-scale density field / cosmology / host dark matter halo mass
For a given cosmology:
Estimate dark matter host halo mass - cosmological context, compare with simulations
Can trace same galaxies (evolving populations) at different redshifts - allows you to connect different surveys and z’s
Constrain galaxy and AGN formation and evolution models
36 SDSS + 16 DEEP2 spectroscopic QSOs in the DEEP2 fields between z=0.7-1.4:
Clustering of DEEP2 galaxies around SDSS QSOs at z=0.7-1.4.
Errors include Poisson errors + cosmic variance.
Similar errors as surveys with 1000s of QSOs (eg. 2dF) through use of cross-correlation with 10,000s of galaxies.
Why measure the cross-correlation? Divide by the clustering of DEEP2 galaxies around DEEP2 galaxies to get the bias of QSO hosts…
Coil et al. 2006 ApJ
The relative bias is 0.9 +/-0.2
Galaxies that host QSOs at z=1 have the same clustering properties (same halo mass) as typical DEEP2 galaxies.
Not as clustered as red galaxies - more like blue galaxies (2s). See using local overdensity / environment measures as well. Constrains host type for QSOs and QSO lifetimes!
No dependence is seen on magnitude or redshift or scale.
Coil et al. 2006 ApJ
EGS is 0.5 deg2: 2ox0.25o
~46x6 Mpc/h at z=0.5 ~80x10 Mpc/h at z=1
z=0.2-1.5 have ~10,000 galaxies and (so far) ~200 Chandra sources with z’s to use to measure cross-correlation with galaxies as a function of both color and magnitude
X-ray AGN are seen to be red or blue+massive
Nandra et al. 2006 ApJL
Coil et al. in prep
Competing QSO/AGN formation/evolution models predict different clustering properties, through assumed accretion and lifetimes:
- all begin with major mergers
1. Kauffmann and Haeneltpredict a strong luminosity-dependence to AGN clustering, based on assumed lightcurve and gas mass accreted ~ host halo mass, leads to luminosity~halo mass - doesn’t fit the data!
2. Lidz, Hopkins et al.predict less luminosity-dependence, as the light curve is not exponential, bright/faint QSOs are similar objects - but their typical host halo masses at z~1 higher than we find
3. Croton et al. follow the Kauffmann and Haenelt model, but include ‘radio mode’ for AGN, where galaxies in halos above a threshold mass can not accrete gas - shuts off SF and black hole accretion. Predict blue galaxies have QSOs at z~1and fainter AGN in red galaxies - in good agreement with our results.
Our results favor galaxies undergoing a QSO phase before settling on the red sequence with a lower luminosity AGN.
Measuring QSO/AGN clustering in fields with galaxy redshifts allows cross-correlation (small scales and with low errors) and local environment measures. Can also compare with red and blue galaxies at the same redshift and in the same volume.
To not be dominated by cosmic variance you need wide areas (few degrees) and multiple fields. However, in comparisons to galaxies in the same volume (cross-correlations, environment) cosmic variance roughly cancels.
Clustering of QSOs/AGN constrains lifetimes, host halo mass, host galaxy type and differentiates between formation models, especially if have wide luminosity range. Caveat: have to know if you’re seeing all QSOs/AGN or if there are sample biases.